Oxidative dehydrogenation catalysts

ABSTRACT

OXIDATIVE DEHYDROGENATION CATALYST COMPRISING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT OR IRON IN COMBINATION WITH TIN, PHOSPHORUS, COMBINDED OXYGEN AND, OPTIONALLY, AN ALKALI METAL MATERIL, IS SUBSTANTIALLY IMPROVED BY IMPREGNATING SUCH CATALYST WITH ADDITIONAL TIN.

nited States Patent Oflice Patented Jan. 29, 1974 3,789,017 OXIDATIVEDEHYDROGENATION CATALYSTS Darrell W. Walker, Bartlesville, kla.,assignor to Phillips Petroleum Company No Drawing. Filed May 6, 1971,Ser. No. 140,970 Int. Cl. 1301i 11/82 US. Cl. 252-437 7 Claims ABSTRACTOF THE DISCLOSURE Oxidative dehydrogenation catalyst comprising at leastone metal selected from the group consisting of nickel, cobalt or ironin combination with tin, phosphorus, combined oxygen and, optionally, analkali metal material, is substantially improved by impregnating suchcatalysts with additional tin.

The present invention relates to chemical compositions. Moreparticularly, the invention relates to catalyst compositions, theirpreparation and the catalytic processes employing such compositions,e.g., processes for effecting the dehydrogenation of hydrocarbons.

Thermal noncatalytic and catalytic processes for converting organiccompounds to compounds having a higher degree of unsaturation are known.The former are characterized by undesirable side reactions, low order ofconversion and yields and poor selectivity to desired product. Thecatalytic processes are characterized by the particular catalyticmaterial employed and the conditions under which the processes areoperated, e.g., in the absence or presence of oxygen. While a number ofsuch catalytic processes have attained some measure of commercialsuccess, there is a continuing search for better catalytic materialswhich exhibit the high activity, high yields to desired product, highselectivity to desired product, extended longevity, high response toregeneration, especially in the presence of air, and which keepundesirable side reactions to a minimum; all characteristics of gooddehydrogenation catalysts. The vexatious problem constantly faced bythose skilled in the art is the identification and characterization ofthe compositions which are highly efficient dehydrogenation catalysts.

Among the more recently disclosed oxidative dehydrogenation catalystsare those which include halogens or halogen-releasing materials. Suchcatalysts exhibit many disadvantages in regard to equipment corrosionand expense of continuously feeding, recovering and recycling therelatively expensive halogen materials. Halogen-free catalytic materialscontinue to be the most desirable for use in dehydrogenation processes.

A recently discovered catalytic material which has been found useful forthe oxidative dehydrogenation of organic compounds is one comprising acombination of at least one of nickel, cobalt or iron in associationwith tin, phosphorus and combined oxygen. Such a catalyst, for example,a Ni/Sn/P/O composition, has been found to be effective for convertingparaffins, such as butane, to useful olefins and diolefins such asbutenes and butadiene. For simplicity, the nickel, cobalt and iron groupis referred to as the ferrous metals of Group VIII, or merely as theferrous metals. The elements contained in the catalyst are notnecessarily in the elemental state but can be combined with sufficientoxygen to form one or more neutral compounds such as nickel stannate,cobalt phosphate, iron stannate, nickel oxide, iron oxide, etc.,depending upon the proportions of the elements present. Such catalystsgenerally have compositions such as shown in the following table:

Weight percent Element Broad Preferred 26-75 3045 n 1-50 14-35Phosphorus. 0. 5-10 2-6 The percentages shown in the table above arebased on the total weight of the catalyst composition, and thedifference between the total weights of the above-named elements andpercent is made up by its combined oxygen content in an amountsufiicient to satisfy the valences of each of the elements in thecatalyst.

It has now been discovered that the above-described ferrous metal/tin/phosphorus/ oxygen catalyst can be still further improved, particularlyin its ability to maintain a high selectivity to desired products over along period of time, by subjecting the catalyst to an additionaltreatment in which 0.1-10, preferably l-S, weight percent of additionaltin is deposited on the catalyst by impregnation. Thus, tin isintroduced into the invention catalyst in two increments: The bulk ofthe tin is first associated with suitable ferrous metal compounds andsuitable phosphorus compounds to the point where it is formed in thedesired physical shape and calcined; then the calcined ferrousmetal/tin/phosphorus/oxygen catalyst is given a final impregnation witha suitable tin compound to provide the activity-stabilizing benefits.After this final impregnation, the improved catalyst is again calcinedat elevated temperatures in an oxygen-containing gas.

The ferrous metal/ tin/ phosphorus/ oxygen catalyst compositions whichare subjected to the impregnation step according to the presentinvention can be prepared by any suitable method. Conventional methods,such as coprecipitation, impregnation, or dry mixing, can be used. Ingeneral, any method can be used which will provide a compositioncontaining the above-described elements in the above-describedproportions and which will have a catalytic surface area of at least onesquare meter per gram. Thus, a ferrous metal compound, a tin compoundand a phosphorus compound can be combined in any suitable way.Substantially any ferrous metal, tin and phosphorus compound can beemployed in the preparation so long as none of the compounds aredetrimental to the final oxidative dehydrogenation catalyst and so longas other elements in the preparation compounds are substantially removedfrom the final catalyst composition by prior washing or byvolatilization. In some instances, however, small amounts of some ofthese other elements, which are involved in the preparation of thecatalyst, can be tolerated in the final catalytic composition. Forexample, if a sulfate such as nickel sulfate or tin sulfate is employedin the preparation, small residual amounts of sulfur can be tolerated.Similarly, the presence of minor amounts of alkali metals, such aspotassium, sodium and the like, can be tolerated and can also be foundbeneficial in some instances. Moreover, minor amounts of arsenic cansometimes be advantageous when included in the catalyst composition.Generally, however, the preferred ferrous metal, tin, and phosphoruscompounds are either the oxides of these elements or compoundsconvertible to the oxide on calcination. Some examples of these arenickel nitrate, cobalt acetate, iron oxide, phosphoric acid, nickelstannate, ammonium phosphate, and the like, including mixtures thereof.

In one suitable method of catalyst preparation, suitable ferrous metalcompounds are coprecipitated with suitable tin compounds by mixingsolutions of these compounds. The coprecipitation can be aided by theaddition of an inorganic base such as an alkali metal or alkaline earthmetal hydroxide to maintain the pH of the mixture above about 7. Theprecipitate is then filtered, washed of any extraneous ions, and then,either before or after drying, impregnated with a suitablephosphorus-containing compound such as phosphoric acid. This compositeis then activated by calcination in an oxygen-containing gas such as airat a temperature of 9001800 F. for 1-24 hours or until the catalyst hasactivity for oxidative dehydrogenation. The solid catalyst compositioncan be conventionally formed in any conventional shape or form such astablets, extrudates, granules, powder, agglomerates and the like.

These compositions can also be supported on or diluted with conventionalcarrier materials such as silica, alumina, boria, magnesia, titania,zirconia, and combinations thereof, as well as other similarconventional carrier materials.

The above-described ferrous metal/tin/phosphorus/oxygen catalyst isthen, according to the present invention, impregnated with an additionalactivity-stabilizing amount of tin using any suitable impregnationmethod known in the catalyst art. Generally, speaking, a solutioncontaining a soluble tin compound is contacted with the catalyst underconditions such that the desired amount of tin-containing liquid isabsorbed by the catalyst. The catalyst is then dried and calcined aspreviously, in an oxygen-containing gas such as air, or merely subjectedto the high temperature and oxygen-containing conditions of theoxidative dehydrogenation reaction zone.

Suitable tin compounds for impregnation are those compounds which areconvertible to the oxide on calcination such as tin oxalate, tintartrate, and the like. Also suitable are other thin compounds which donot leave undesirable residues on the catalyst. As mentioned above,minor amounts of sulfur residue on the catalyst are tolerable and, thus,tin compounds such as tin sulfate are satisfactory. Although lesseconomical, nonaqueous solutions containing organo soluble compounds,for example, tetraphenyltin, can also be used for the impregnation.Because halogen residues are generally considered objectionable, tinhalides are not preferred impregnating compounds.

Following impregnatiton, the tin-treated composite can be dried attemperatures in the range of 100 to about 400 F. and/ or preferablycalcined at temperatures of 800 to 1200 F. or higher, e.g., 1800 to 2500F.

The thus-modified tin-impregnated catalysts have been found to beparticularly useful for the oxidative dehydrogenation of hydrocarbonfeedstocks having from about 2 to about 12 carbon atoms per molecule andat least one grouping, i.e., adjacent carbon atoms having at least onehydrogen atom on each carbon. Such compounds can be branched orunbranched and include paraffins as well as monoolefins, but parafiinsare presently preferred. The conversion of butane to 1,3-butadiene hasbeen found particularly advantageous b the processes of the inventionusing these tin-modified catalysts. Some specific examples of otherfeeds include ethane, propane, isobutane, pentane, isopentane, hexane,Z-methylhexane, octane, 2,4-dimethyloctane, butene-2, 2-methylbutene-1,hexene-Z, octene-l, 3- methylnoneen-4, dodecene-l, and the like,including mixtures thereof. The conversion products are valuablecompounds particularly useful as intermediates for the preparation ofpolymeric materials such as synthetic rubbers and the like.

The hydrocarbon feedstocks can be dehydrogenated according to theprocesses and with the modified catalysts of the present invention attemperatures in the range of from about 800 to about 1200 F., preferablyfrom about 950 to about 1150 F., at any convenient pressure such as fromabout 7 to about 250 p.s.i.a., and and at a hydrocarbon:oxygen ratio offrom about 110.5 to about 1:4. The presence of steam is frequentlybeneficial and steam:hydm carbon ratios up to about 50:1 can be used.The hydrocarbon feed rate will generally be in the range of from about50 to about 5,000 GHSV. The fixed catalyst bed is the preferred mode ofcontact, but other modes, such as the fluidized bed, can also be used.

The dehydrogenation processes of this invention are ordinarily carriedout by forming a mixture, preferably a preheated mixture, of thehydrocarbon feed, the oxygencontaining gas and the steam (if used) andpassing this mixture over the catalyst at the desired temperature. Theefiluent from the reaction zone is subjected to any suitable separationmethod to isolate and recover the desired product. Unconverted feeds orpartially converted materials can be recycled.

Generally, at least trace amounts of oxygenated products are also formedin these reactions. For example, compounds such as furan, acetaldehyde,furfural and acetic acid can be obtained. Some carbon oxides will beformed, as well as some cracking products.

The catalytic materials of the invention can operate for extendedperiods before regeneration is required. However, if and when suchregeneration is required, this can be accomplished readily b simplystopping the flow of hydrocarbon feed. Contact of the catalytic materialwith air and steam can be maintained at process operating conditionsuntil activity of the catalyst is restored.

The invention can be illustrated by the following examples.

EXAMPLE I Preparation of Catalysts A Ni/Sn/P/O catalyst was prepared bypreparing separate aqueous solutions of 1160 g. NiNO -6H O, 400 g. K SnO-3H O, and 289 g. KOH percent). The three solutions were then added,simultaneously and dropwise, into a stirred container of water whilemaintaining a pH of about 8-9. The resulting wet gel was filtered andwashed sufiiciently with distilled water to reduce the potassium contentto the desired level. The wet gel was then intimately mixed with anaqueous solution containing 62 g. of H PO (85 percent). The mixture wasthen dried at 220 F., calcined at ll00 F. for 3 hours, then crushed andscreened to a 20-40 mesh size. The Ni/Sn/P/O composition contained 42%Ni, 27% Sn, 3.1% P, and 0.63% K, by weight. It had a surface area ofmfi/g.

A 5 g. portion of the above material was impregnated with an additional2.5 weight percent Sn by slurrying with 10 cc. of an aqueous solutioncontaining 0.225 g. SnSO It was then dried at 220 F. and calcined at1100 F. for 3 hours.

As a control, still another 5 g. portion of the above Ni/Sn/P/Ocomposition was mixed with 10 cc. of water containing no impregnant. Itwas also dried at 220 F. and calcined 3 hours at 1100 F.

EXAMPLE II Oxidative Dehydrogenation of Butane Each of the two catalystsprepared in Example I was used in the oxidative dehydrogenation ofbutane in separate runs. The runs were carried out in a fixed bedreactor at 1100 F. and at atmospheric pressure. The space rates for thebutane, oxygen and steam were 500, 530 and 5,000, respectively. Theefilunt was sampled after l8 hours and again after 65 hours. The resultsof these runs are shown in Table I.

TABLE I.OXIDATIVE DEHYDRO GENATION F BUTANE Catalyst Ni/Sn/P/O Ni/Sn/P/O(with additional (no additional 2.5% Sn) Sn impregnation) On-stream, hrs18 65 18 65 Conversion, percent 40. 39. 3 41. 8 40. 0 Yields, molpercent:

Butadiene.- 19. 6 18. 8 19. 7 16. 8 Butenes 6. 0 8.5 7. 4 10. 3 Cracked-4. 1 4. 0 5. 0 5. 1 M Oxidiz ed 10. 9 8. l 9. 7 7.9

odivity, ercent to- Butadi neuui 4s. 4 47. 7 47. 2 42. o Butenes andbutadiene 63. 1 69. 4 65.0 67. 7

1 Modivity is a simplified selectivity based on analysis of gas phaseproducts for converted hydrocarbons, oxides of carbon and unconvertedfeedl.1 As reported herein, conversions and yields are on same basis asmo Way.

The data in Table I show that over the on-stream period from 18 to 65hours, there was a relatively small change in catalyst activity with theinvention catalyst containing the small amount of additional impregnatedtin. There was, however, a more substantial decrease in activity overthis period with the noninvention catalyst. The decrease in activity wasevident in the conversion, but particularly in the selectivity andyields to butadiene. These data show the activity-stabilizing effects ofthe invention catalyst and process.

While certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifications or embodiments of the invention will be apparent tothose skilled in the art in view of this disclosure. Such modificationsor embodiments are within the spirit and scope of the disclosure.

I claim:

1. A method for stabilizing a catalyst for the dehydrogenation ofhydrocarbon feedstocks containing from 2 to 12 carbon atoms, saidcatalyst consisting essentially of from about 30 to about 45 weightpercent, based on weight of catalyst, or at least one ferrous metalselected from the group consisting of nickel, cobalt and iron inassociation with from about 14 to about 35 weight percent, based onWeight of catalyst, of tin and from about 2 to 6 Weight percent, basedon weight of catalyst, of phosphorus and wherein at least one of saidferrous metal, tin or said phosphorus is combined with oxygen; whichmethod comprises treating a calcined catalyst having the describedcomposition with a tin-containing material to impregnate said calcinedcatalyst with from about 0.1 to about weight percent, based on weight ofcatalyst, of additional tin, and thereafter calcining said catalystimpregnated with additional tin.

2. A method of preparing an oxidative dehydrogenation catalyst whichcomprises:

forming a catalytic composite material consisting essentially of fromabout 30 to about 45 weight percent, based on weight of catalyst, of atleast one ferrous metal selected from the group consisting of nickel,cobalt and iron in association with from about 14 to about 35 weightpercent, based on weight of catalyst, of tin and from about 2 to about 6weight percent, based on weight of catalyst, of phosphorus and whereinat least one of said ferrous metal, said tin or said phosphorus iscombined with oxygen; calcining said composite; contacting said calcinedcatalytic composite material with a tin-containing material toimpregnate said catalyst with 0.1 to 10 weight percent additional tin;and

calcining said composite impregnated with additional tin.

3. A method according to claim 2 wherein the temperature at which saidcatalytic composite material is calcined is in the range of 900 to 1800F.

4. A method according to claim 3 wherein said temperature at which saidcomposite impregnated with additional tin is calcined is in the range of900 to 1800 F.

5. An oxidative dehydrogenation catalyst prepared according to themethod of claim 2.

6. A method according to claim 2 wherein said catalytic compositematerial contains 42 weight percent nickel, 27 weight percent tin, and3.1 weight percent phosphorus, and wherein said calcined catalyticcomposite is impregnated with 2.5 weight percent additional tin.

7. A method of preparing an oxidative dehydrogenation catalyst Whichcomprises:

forming a catalytic composite material consisting essentially of 42weight percent nickel, 27 weight percent tin and 3.1 weight percentphosphorus, wherein at least one of said nickel, tin and phosphorus iscombined with oxygen;

calcining said composite;

contacting said calcined catalytic composite with a tincontainingmaterial to impregnate said catalyst with 2.5 weight percent additionaltin; and calcining said composite impregnated with tin.

References Cited UNITED STATES PATENTS PAUL M. COUGHLAN, JR., PrimaryExaminer U.S. Cl. X.R. 260680 E, 683.3

